A conventional tandem solar cell is made by stacking two or more solar cell devices with the same energy gap or different energy gaps, so as to fabricate a tandem solar cell module. In the design, the solar cell device absorbing high energy spectrum is generally placed at an upper layer, and the solar cell device absorbing low energy spectrum is placed at a bottom cell. The sunlight spectral energy is absorbed layer by layer through different materials of light absorption layers, so as to improve the efficiency of the cell module.
With a silicon crystal solar cell, which has the largest market share currently, as an example, to effectively utilize the incident light with short wavelength which is not absorbed by the silicon crystal solar cell, the cell with a wide energy gap higher than the silicon crystal is stacked above the silicon crystal solar cell, so as to improve the efficiency of the cell module. However, the design of the electrode of the cell at the upper layer is generally based on an entire surface transparent conductive oxide (TCO), and the purpose is to make the upper cell become a transmission type cell device, such that the spectrum with long wavelength passes through the upper cell and then reaches the bottom cell (the silicon crystal cell) to be absorbed. Thus, not only the absorption layer of the upper cell can absorb the incident light with short wavelength, but also the entire surface transparent conductive oxide electrode of the upper cell can shield or absorb parts of the light. It may cause the reduction of the amount or the intensity of incident light entering the silicon crystal cell, which is not helpful for the absorption of the material of the light absorption layer at the bottom cell.